Catalytic reactor vessels having one or more fixed catalyst beds are now commonly filled by using a catalyst distributor. Such a technique is known as Catalyst Oriented Packing (frequently referred to as COP loading) and is particularly useful to produce uniformity in the permeability and overall density of the catalyst bed. In current catalytic processing, catalyst particles are generally manufactured by extrusion in the form of cylindrical rods of 1/32" to 1/4" diameter. The rods are then broken into lengths having a diameter to length ratio of about 1 to 4. Such extrudates are typically formed of alumna, silica-alumna or synthetic or natural zeolitic materials and are substantially less expensive to produce then spherical catalyst. However, such extrudate particles have a high angle of repose; the angle at which a free-standing pile of material is stable. Consequently, they are difficult to distribute evenly over a large diameter cylindrical vessel. Further, due to differences in size of such particles, as well as chipping and breaking during both manufacture and loading into a process reactor, they tend to "classify" or separate if the bed is filled by gravity alone from a central point in the vessel.
The primary purpose of COP loading is to minimize void spaces and consequently local "hot spots" which can occur during exothermic reactions of hydrocarbons with the catalyst particles. Additionally, increased packed density of the solid particulate material, catalyst particles, improves the flow distribution of reactants within the vessel. Further, increased bed density limits settling of the bed when the reactor is brought on stream and subjected to hydraulic forces by fluid flow through the reactor. In general, the amount of catalyst can be increased several percent in an existing vessel. Conversely, several percent less reactor volume is required for the same amount of catalyst in a new vessel.
In general, previously known catalyst oriented-loading apparatus included a distributor disk having a uniform diameter and a plurality of radial blades or fin members of uniform radial length equally spaced from each other circumferentially. Such blades or fins on top of the rotating disk randomly fling catalyst from the edge of the disk with catalyst thrown different radial distances depending upon the radial portion of the blade acting on the particle. In general, the distributor is either a cone shaped member or a flat circular plate. Since the distance the catalyst is thrown is proportional only to the disk speed, the speed of the distributor must be varied in order to distribute catalyst at different radial distances across the entire cross-sectional area of the bed by flinging catalyst from the edge of the disk. Where the disk is a flat plate having vanes formed thereon, a few holes are formed in the plate so that some of the catalyst particles fall directly downwardly through the rotating member toward the center of the reactor vessel.
U.S. Pat. No. 3,804,273, Uhl, is directed to apparatus for loading a catalyst bed with a radial distributor having a single conical surface. The only method of distributing catalyst across the full bed diameter is to increase and decrease the speed of the rotating disk. A particular disadvantage of a conical surface is that, depending on the angle of the cone, speed does not greatly vary the width of the catalyst ring that can be cast from its edge. Accordingly, the utility of such disks is generally limited to small diameter vessels.
U.S. Pat. No. 3,972,868, Johnson, et al., discloses a flat disk having vanes and a plurality of slots or holes through which some of the catalyst may fall near the center of the bed; the remainder of the catalyst is thrown toward the vessel side. This system also requires variation is the speed of the rotating disk to load catalyst so that it covers the entire level of a catalyst reactor bed.
A particular disadvantage of such prior flat disk arrangements lies in the fact that at a given speed the catalyst is thrown by a few fins or radial ribs into a circular or annular mound which tends to classify catalyst particles falling on it. The larger particles roll to the bottom and outside of the mound while the smaller particles stop on the mound itself. While to a certain extent, these difficulties are alleviated by varying the speed of the rotating disk, slowing disk speed significantly increases the loading time for the reactor bed, because loading rate is in general proportional to such speed. On the other hand, high speed of such a disk having only a few fins or vanes results in catalyst flying off the disk without sufficient residence time for the fins to contact and control the radial throw distance of the particles. Additionally, it is difficult to control disk speed to achieve a desired variations in radial throw distance because the interior of the vessel above such a bed is usually too full of dust to permit the operator to actually see the catalyst bed from the loader. Accordingly, it is necessary to determine the probable level of distribution by the number of drums of catalyst that have been loaded at a given bed level. Such a procedure is time-consuming and not necessarily accurate enough to permit level filling of the bed. In fact, it is general practice to fill the bed at the outer edge higher than necessary (say 6 to 12 inches); and then by slowing the speed of the distributor disk, the height of the center of the bed is filled to a level above that at the outer edge by a similar amount. The speed is alternately increased and decreased up the reactor as the depth of the bed or beds is increased throughout the reactor. The problem is further aggravated where the vessel contains several separate beds, each supported by a separate support "screen" forming "vessel internals" so that the lower beds must be filled through accessways in the center of the overlying bed support. Visual inspection is thus made more difficult.
U.S. Pat. No. 4,306,829, Loutaty, et al., discloses a distributor for catalyst particles in a reactor or grain storage in a silo. The distributor includes flexible straps pivotally supported by hooks along the length of a drive shaft. The straps may be formed of reinforced rubber and are either of equal length or progressively longer away from the feed hopper discharge. The examples indicate the system to be satisfactory for filling a model of a reactor vessel 60 cm (about 2 feet) in diameter. It appears that the active lengths of the rotating straps vary in diameter with the speed of the drive shaft and their interaction with falling catalyst particles. Efficient loading of vessels with each of the above-noted arrangements has been limited to relatively small diameter reactors, for reasons noted above.
U.S. Pat. No. 4,433,707, Farnham, assigned to the assignee of the present invention, discloses a method and apparatus for uniformly filling a reactor vessel at each level with an even distribution of catalyst particles from the center of the vessel to its outer wall by using a plurality of axially spaced disks of differing diameters rotated at the same speed by a single drive shaft. Desirably, three conical disks are sued with the largest diameter nearest the supply hopper feed tube. The upper disks include a central opening to permit catalyst to be fed to each of the lower disks. Because the disks are of different diameters, each spreads catalyst to a different area around the vessel with the drive shaft rotating at constant speed. Each disk includes vanes equally spaced circumferentially from each other to fling or cast catalyst into three bands. Such a system is quite satisfactory for delivery of catalyst to vessels of smaller diameter and deep beds, where adequate "head" room is available at the top of the vessel or the internal bed supports above each of several beds. However, the method is also limited to laying down only a few annular rings simultaneously, without changing rotor speed.
Federal Republic of Germany Patent 2,703,329 issued March, 1978 disclosed another particle loading system using axially spaced multiple disks rotated by a common drive shaft. The mode of operation is similar to the above-noted Farnham patent.
West German patent application 1,457,867 filed Dec. 29, 1964 (laid open Aug. 12, 1971) discloses a fertilizer spreader which includes three stepped disks of different diameters. Each disk includes curved vanes of differing lengths. Alternatively, a single disk includes six segments, each having a radially tapered diameter with three different curved slinger vanes. The three vanes of each disk or segment have different curvatures and slopes to further assure overlap of the bands of fertilizer laid down simultaneously. The longer vanes in either form have a higher angle to the vertical axis of the disk and smaller curvature in the plane of the disk than the other two sets of vanes. The shortest vanes correspondingly have a lower angle to vertical and a larger radius of curvature in the disk plane. The intermediate length vanes are likewise intermediate the vertical angle and radius of curvature of the other two vanes. Each vane, whether on a single disk or on three disks, begins at a different radial distance from the axis of the disk. This also assures the desired coaxial overlap of the three bands of fertilizer laid down on the earth's surface as the spreader moves transverse to the axis of rotation of the disk, particularly in additional passes of the distribution over the same surface area. Because the area covered during any transverse of the distributor must overlap any annular ring that might be laid down, there is no teaching or suggestion that the disk area between the vanes be proportional to the area of the distributed fertilizer. Accordingly, there is no disclosure or suggestion of laying down concentric bands of catalyst with minimum overlap in a closed vessel without changing speeds of the disk and without transverse movement of the disk.